Well for one thing, Americans enunciate all their letters clearly; especially their "r's". I'm sure you'll struggle with our (one thing I do have in common with Ozzies) silent "r's". I say this because I have an American friend who moved here just a month before I did and she kept saying that that was her biggest difficulty. She said that that made it difficult for her to understand what was being said. For me it's the speed and tempo. But I have to say that I sometimes think she is saying "can" when in fact she's saying "can't". As you know our can't rhymes with aren't (without pronuncing the r though, lol...can't think of a better rhyming word). Other than that I have no problem understanding her; and funny enough she understands me just fine too :-)